Integrated image rejection frequency converter

Abstract: A 3-element series parallel resonator (40), which performs series resonance and parallel resonance at a predetermined frequency by a combination of three elements (C1,C2,L1) including an inductor and a capacitor of concentrated constants, is used as a filter. This design can reduce the circuit constant and permits a filter to be formed on a semiconductor substrate. Accordingly, various micro-wave devices, such as an amplifier which requires a filter, a frequency converter, a multiplier and signal switcher, can be designed into an MMIC on a single chip.

Description: The present invention relates to a semiconductor device, and, more particularly, to a semiconductor device having a filter, such as a micro-wave filter, an amplifier, a mixer or a multiplier. Micro-wave devices, such as communication devices, generally use a filter. Fig. 1 is a block diagram showing the structure of an input stage (front end) of a satellite broadcasting direct receiver. A low-noise amplifier (LNA) 2 is connected to an input terminal 1, and its output is input to a band-pass filter 3. The output of the filter 3 is input to a mixer (MIX) 4, which mixes it with the output of a local oscillator (LOC) 5 and outputs the resultant signal to an intermediate-frequency amplifier (IFA) 6. The output of this intermediate-frequency amplifier 6 is output to an output terminal 7. The filter 3 is used to prevent image disturbance and prevent the influence of the image band noise of the low-noise amplifier 2. While it is desirable to design a semiconductor device including such a filter 3 into an IC circuit for miniaturization, the presence of the band-pass filter 3 makes it impossible to design the whole device on one chip. It is therefore inevitable to design the low-noise amplifier 2 alone on a single IC (chip C1) and design the mixer 4, local oscillator 5 and intermediate-frequency amplifier 6 on another single IC (chip C2), thus requiring at least two chips. It is thus difficult to miniaturize the semiconductor device. Alternatively, as shown in Fig. 2, the band-pass filter 3 may be shifted to the preceding stage to the low-noise amplifier 2, thus allowing all the low-noise amplifier 2, mixer 4, local oscillator 5 and intermediate-frequency amplifier 6 to be designed on one chip. The semiconductor device shown in Fig. 2 cannot, however, provide the effect of the filter 3 to remove the influence of the image band noise of the low-noise amplifier 2, and is disadvantageous in lower noise index over the semiconductor device shown in Fig. 1. To overcome this shortcoming, an image rejection type frequency converter as shown in Fig. 3 has been proposed (Japanese Unexamined Patent Publication No. sho 61-208304). As shown in Fig. 3, a first 90-degree hybrid circuit 12 in a signal band of the reception frequency and local oscillation frequency and a second hybrid circuit 18 in an intermediate frequency band are connected together with two frequency converters 13 and 14 in between. A terminal 10 to which an input signal (RF) from an antenna or a signal from the local oscillator (LOC) is input, is connected to the first 90-degree hybrid circuit 12. A terminal 11 to which the signal from the local oscillator is input, is connected to the frequency converters 13 and 14. A terminal 16 from which the intermediate frequency (IF) is output is connected to the frequency converter 13 and the second hybrid circuit 18. The second hybrid circuit 18 is constituted of a dual-gate FET 15. This dual-gate FET 15 has a drain electrode 21, a first gate 22, a second gate 23 and a source 24. Input signals to the 90-degree hybrid circuit 12 are signals HS1 and HS2, which come from the terminal 10 and have a phase difference of 90 degree with respect to each other. The dual-gate FET 15 has an equivalent capacitor provided between the drain electrode 21 and the second gate 23. When a signal is applied to the first gate 22, therefore, a signal phase difference of 90 degree occurs between the aforementioned electrode output signals. The intermediate frequency signal output from the second gate 23 therefore becomes equivalent to the signal that is before the phase shift is accomplished by the hybrid circuit 12. This will cancel out the first phase shift by the hybrid circuit 12, thereby providing an image-rejection type frequency converter. This circuit does not filter out an image signal using a filter, but uses two frequency mixers 13 and 14 to provide two outputs, and mixes both outputs with some phase difference to cancel out the image signal. This design permits the mentioned components to be designed on one chip without using any filter for image rejection. Examples of an IC having a filter located between the low-noise amplifier and mixer are disclosed in IEEE MTT33 No. 11 pp. 1231-1235 and IEEE MMWMC 1992, pp. 101-104. As the frequency to be handled is high, both ICs employ a filter that uses a distributed constant circuit. The former IC employs an open stub as shown in Figs. 4A and 4B, while the latter IC employs a bridge T as shown in Figs. 5A and 5B. Another example of a system that requires a filter is a transmitter-receiver of a portable telephone. Fig. 6 shows a block structure of such a transmitter-receiver of a portable telephone. A duplexer is used for the conventional filter. There are prior arts as shown in Figs. 3 through 5 to design a semiconductor device including a filter into IC. But those prior arts have the following problems. The prior art 1 shown in Fig. 3 cancels out the IF signal, resulting in poor converting characteristic, and is not thus practical. While the prior art 2 shown in Fig. 4 and the prior art 3 shown in Fig. 5 have been studied with their prototypes actually made, they have a shortcoming of an increased chip area due to the use of a distributed constant circuit. For instance, the prior art 2 requires en area of 0.5 mm 2 and the prior art 3 also requires an area of about 0.5 mm 2 . Those problems become prominent in a system that is used in a 1-GHz band, such as a portable telephone. IEEE Journal of Solid-State Circuits, vol. 27, no. 10, October 1992, NY, US; Toshihiko Yoshimasu et al: "A low current Ku-band GaAs monolithic image rejection down-converter" discloses a device according to the pre-characterizing part of claim 1. According to his document the resonators are implemented by a transmission line approach. Microwave Journal, vol. 33, no. 9, September 1990, Norwood, MA, US; Roger Helkey: "A new receiver filter transformation" discloses filters including distributed constant circuits and concentrated constant circuits. It is therefore an object of the present invention to provide a semiconductor device having a filter circuit, which can be designed on a single chip and is used in a filter-incorporated system, and a one-chip IC having that filter circuit incorporated therein. This object is achieved by a semiconductor device according to claim 1. The further claim is related to a different aspect of the present invention. According to the present invention, a semiconductor device including a filter, comprises an input terminal to which an input signal is input; an amplifier connected to said input terminal; a mixer; a local oscillator for inputting a local oscillation signal to said mixer; and one single 3-element series parallel resonator, provided between said amplifier or said mixer and ground, for performing series resonance and parallel resonance at a predetermined frequency by a combination of three elements including an inductor and a capacitor of concentrated constants. A filter embodying the present invention is constituted of a 3-element series parallel resonator having a combination of three elements including concentrated-constant oriented capacitors and inductors. When the filter circuit is designed with a concentrated constant-element there are an infinite number of combinations of capacitors and inductors. To obtain the desired filtering performance, however, a 3-element type will minimize the chip area most efficiently. Fig. 7 shows the relation between the number of resonator elements and the chip area when the band width of the filter and the out of band performance are limited. For a 2-element filter having series or parallel resonators each using one capacitor and one inductor, the pass band or device band can be designed as shown in Figs. 8A and 8B. To make the band width narrower to improve the out of band characteristic, it is necessary to use an inductor having a significantly large inductance, so that the chip size becomes large while the number of elements is small. For instance, in constituting a filter which will pass 910 to 956 MHz, and has a block band of 810 to 826 MHz and a block amount of 50 dB, an inductance L needs to be 60 nH for a 2-element filter, whereas the inductance L of 20 nH is sufficient for a 3-element filter. For a 4-element filter or a filter having more than four elements, the number of elements increases and the chip size becomes greater than that for the 3-element type. Therefore, the 3-element type will provide the desired filter characteristic with the smallest area. A narrow-band filter may be designed with a combination of 3-element series parallel resonators, and will have the minimum area as a filter having a similar performance. There are four possible combinations of 3-element series parallel resonators 31, 32, 33 and 34 comprising three elements including an inductor L and a capacitor C, as shown in Figs. 9A, 9B, 9C and 9D. When those 3-element series parallel resonators 31, 32, 33 and 34 are combined as shown in Figs. 10A, 10B, 10C and 10D, the pass band and device band can be designed independently. Although two resonators are used for shunt and one resonator for series, a total of three resonators, in the examples of Figs. 10A to 10D, one resonator may be used for shunt and for series, or two or more resonators may also be used. According to this invention, a filter is constituted by the above-described 3-element series parallel resonators and a combination thereof, allowing a filter-incorporated system to be designed on a single chip which could not be accomplished by the prior arts. Fig. 1 is a block diagram showing the input stage of a satellite broadcasting direct receiver; Fig. 2 is a block diagram showing the input stage of another satellite broadcasting direct receiver; Fig. 3 is a block diagram of prior art 1; Figs. 4A and 4B are pattern diagrams of prior art 2; Figs. 5A and 5B are pattern diagrams of prior art 3; Fig. 6 shows the block diagram of a portable telephone; Fig. 7 is a diagram showing the relation between the number of elements in a resonator and the chip area; Figs. 8A and 8B are circuit diagrams of 2-element filters; Figs. 9A through 9D are circuit diagrams of 3-element filters; Figs. 10A through 10D are diagrams showing combinations of 3-element filters; Fig. 11 is a circuit block diagram of a first embodiment of the present invention; Fig. 12 is a pattern diagram of the first embodiment; Fig. 13 is a circuit block diagram of a further converter; and Fig. 14 is a pattern diagram of the converter of Fig. 13. Preferred embodiments of the present invention will now be described referring to the accompanying drawings. Fig. 11 is a block diagram showing the structure of a first embodiment of the present invention as applied to a satellite broadcasting transmission/reception converter. As shown in Fig. 11, an input terminal 1 is connected to the input end of a low-noise amplifier 2 whose output end is connected to a frequency mixer 4. A local oscillator 5 is connected to this frequency mixer 4 whose frequency-mixed signal is output to an intermediate-frequency amplifier 6. A signal amplified by the intermediate-frequency amplifier 6 is output from an output terminal 7. In this embodiment, a 3-element series parallel resonator 40 is connected between the low-noise amplifier 2 and the frequency mixer 4. This 3-element series parallel resonator 40 has a series circuit of a capacitor C1 and an inductor L1 and a capacitor C2 connected in parallel. The satellite broadcasting reception converter performs frequency mixing of a weak signal of 12 GHz from a satellite with a signal of 10.7 GHz from a local oscillator 5, and outputs a signal of 1.3 GHz which is the difference between the input signal frequency and the local oscillation frequency. In this case, the frequency of a signal of 9.3 GHz becomes an image frequency, so that a filter for eliminating the signal of 9.3 GHz without attenuating the signal of 12 GHz should be provided in the preceding stage of the frequency mixer 4. As the 3-element series parallel resonator 40 is connected between the low-noise amplifier 2 and the frequency mixer 4 in this embodiment, parallel resonance will be caused by the input signal frequency of 12 GHz and series resonance will be caused by the image frequency of 9.3 GHz if the inductor L1 is set to 1.0 nH, the capacitor C1 to 0.2 pF and the capacitor C2 to 0.5 pF. Fig. 12 shows a pattern diagram of the circuit of Fig. 11. In the 3-element series parallel resonator 40 which constitutes a filter in this embodiment, the inductor L1 can be formed by a spiral inductor, and the capacitors C1 and C2 by MIM capacitors. This permits a desired filter to be designed with an area of about 0.1 mm 2 . Through evaluation on prototypes, it is found that this filter can accomplish image rejection of 15 dB or above. This characteristic is better than that of the prior art 2, with a chip area being 1/5 of that of the prior art 2. Fig. 13 is a block diagram showing the circuit of a further converter, and Fig. 14 is a pattern diagram of this circuit. In this converter, two 3-element series parallel resonators 40 and 41 are used in the combination as shown in Fig. 10B. More specifically, in addition to the 3-element series parallel resonator 40, the 3-element series parallel resonator 41 is connected between the output end of the low-noise amplifier 2 and the input end of the mixer 4 in this converter. In this converter, image rejection of 30 dB or greater can be accomplished by setting the inductor L1 to about 1 nH, the capacitor C1 to about 0.2 pF, the capacitor C2 to about 0.5 pF, the inductor L2 to about 1 nH, the inductor L3 to about 1 nH, and the capacitor C3 to about 0.2 pF. The filter portion could be constituted with an chip area of 0.15 mm 2 . The acquired performance is the same or better than that of the filter of the prior art 3 shown in Figs. 5A and 5B, and the chip area is 1/3 of that of the prior art 3. According to the present invention, as described above, the filter area can be reduced to 1/3 to 1/5 of that of the prior arts by using a 3-element series parallel resonator as a filter, and a filter-incorporated system will be designed into a one-chip IC with a practical chip size. The filter using a 3-element series parallel resonator according to this invention is effective not only in a satellite broadcasting receiver as discussed in the foregoing description of the embodiment, but also in designing other filter-incorporated systems into IC circuits.

Claims: A semiconductor device including a filter comprising: an input terminal (1) to which an input signal is input; an amplifier (2) connected to said input terminal; a mixer (4), an input end of which is connected to an output end of said amplifier (2); a local oscillator (5) for inputting a local oscillation signal to said mixer (4); characterized by comprising: one single 3-element series parallel resonator (40) connected between said output end of said amplifier (2) or said input end of said mixer (4) and ground for performing series resonance and parallel resonance at a predetermined frequency by a combination of three elements (C1, C2, L1) including an spiral inductor and a concentrated-constant-element MIM capacitor; said amplifier (2), said mixer (4) and said 3-element series parallel resonator (40) being provided on a single chip; said 3-element series parallel resonator (40) has an inductor (L1) and a first capacitor (C1) connected in series to said inductor (L1), and a second capacitor (C2) connected in parallel to the series circuit of said inductor (L1) and said first capacitor (C1). The semiconductor device according to claim 1, characterized by further comprising an intermediate-frequency amplifier (6) for amplifying an intermediate-frequency signal output from said mixer (4), and an output terminal (7) to which an output signal of said intermediate-frequency amplifier is applied.

Inventors: MIYA TATSUYA, NOGUCHI TSUTOMU, MIYA, TATSUYA, NOGUCHI, TSUTOMU, MIYA, TATSUYA, C/O NEC CORPORATION, NOGUCHI, TSUTOMU, C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1994
Main classification: H03D7
IPC codes: H03D7